Pressure transducers conventionally include pressure sensor headers. U.S. Pat. No. 4,695,817 entitled, ENVIRONMENTALLY PROTECTED PRESSURE TRANSDUCERS EMPLOYING TWO ELECTRICALLY INTERCONNECTED TRANSDUCER ARRAYS issued to A. D. Kurtz et al. on Sep. 22, 1987 and assigned to the assignee herein, the entire disclosure of which is hereby incorporated by reference herein, provides an example. Certain pressure sensor headers include a metal header shell having a front face with straight or tapered holes and header pins extending therethrough. Well known fused glass-metal seals sit in the holes and seal the header pins to the front face of the header shell. Pressure sensor headers commonly operate under external pressures, for example hydrostatic pressures, which can reach extremes, depending on the sensor application, up to and in excess of 50,000 psi.
Referring now to FIG. 1A, there is shown a graphical representation of an operation of a pressure sensor header 10 under a hydrostatic pressure that exposes a front face 12 of a metal header shell 11, as well as the cylindrical side wall 14 of the header shell 11, to pressure forces. The pressure force N acting on the header shell's cylindrical side wall 14 generates compressive tangential and radial stresses (hoop stress) in the side wall 14. The pressure force F acting on the front face 12 of the header 10 pushes on the glass seals 16 and header pins 18. An excessive amount of pressure force F on the front face 12 of the header 10 can push the pins 18 or glass seals 16 into the header 10, breaking the glass-metal seals 17 and allowing leakage. The compressive hoop stress generated in the side wall 14 of the header shell 11 compresses or constricts the seals 16 around the pins 18 thereby strengthening them. Under even greater hydrostatic pressures, the compressive hoop stress assists in retaining the seals 16 or preventing leaks, than if the side wall 14 of the header shell 11 were not exposed to any hydrostatic pressure.
Referring now also to FIG. 1B, the pressure force N acting on the side wall of the header shell functions similarly to the frictional forces between the glass seals 16 and the walls 19 of the header pin apertures 15. The frictional forces resist the motion, or pushing out, of the glass seals 16 from the pin apertures 15.
The pressure sensor header is ordinarily welded to a port or other transducer element using a weld area that is typically modeled as a thick wall cylinder. To survive these high stresses under pressure, such a weld area requires the use of a deep, penetrating butt joint weld. Such deep welding processes usually produce localized heat in the header material, which may stress or crack the glass header seals, pins and other header components. Typical design strategies for avoiding such problems involve moving the pins and other components away from the zone affected by the welding heat. Such designs often involve making the header larger, or longer in length.
However, these conventional pressure sensor header to port joining methods still present various problems. The extreme external pressures tend to fatigue and fracture the welded joints at the header-port interfaces. Additionally, as described above, the weld heat during the joining process tends to heat and damage the glass seals. The provision of larger or longer headers to avoid such weld damage may result in more costly, heavier or less accurate pressure headers.
Thus, an improved method of joining the pressure sensor header with a port or other transducer element is desired, which provides a higher strength device that can operate under extreme applied pressures, while also avoiding damage to header components during the joining process.